Female football fans were asked to show their bras to stewards during security searches, a supporters' group has said.
Grimsby Town fan group the Mariners Trust made the allegation in a letter to Stevenage FC after the two sides met on Saturday.
It said some fans wearing underwired bras were also asked by stewards at the Lamex Stadium if they could feel them.
Stevenage FC said its risk assessment found "high-risk groups attending and potential for anti-social behaviour".
The stewarding plan for the match was "not typical" of those at Stevenage, it said.
The club said after liaising with Grimsby Town's safety officer and the police it was thought prohibited items were likely to be brought into the ground and could be passed on to those "deemed less likely to be searched, such as women and younger supporters".
No incidents were recorded on the day of "inappropriate behaviour" towards female supporters or young spectators, it said.
However the club would study CCTV footage and investigate to see infringements of procedures had not taken place, it added.
The checks, carried out by female stewards, but which the supporters' trust said were "in full view of male stewards, fans and police", have been described as "a gross invasion of privacy".
The letter from the supporters' group alleges stewards asked some female fans "if they could feel their bras" if they told them their bras were underwired.
The group says children as young as five were subjected to full body searches and supporters had items that were not listed as being banned confiscated, such as "contact lens solution, cough sweets and medication".
The letter also said a female steward was posted inside a male toilet, adding: "The steward was asked to leave by Grimsby Town supporters, but she refused despite the fact several male stewards and police officers were stood outside."
Paul Savage, board member of the Mariners Trust, told the BBC he had been among 800 supporters queuing to enter the ground.
He said the woman who were asked by stewards to show their bras ranged in age between "mid-30s to 70-year-olds". He added the women declined the request.
"They were all shocked and because of the nature of the request, they were stunned and until they got into the ground, they didn't know what to do and say, "he said.
"It was only later on when we got word about what had happened that we tried to take it further."
The Mariners Trust described the treatment of supporters as "amongst the worst our fans have experienced in decades of travelling across the world to watch football."
The letter concludes by calling on Stevenage FC to address the "serious failings" as a "matter of urgency... to ensure no other visiting team's supporters are treated as animals in the way your club did on Saturday
The English Football League said it "had been made aware of the contents" of the supporters' letter and a statement by Stevenage FC.
"The EFL's security advisor is looking further into the matters raised and will be seeking the observations of both clubs."
The league would not make any further comment until all the facts had been "fully considered", it said.
Hertfordshire Police said it had not been contacted by supporters, but any complaints would be would "fully investigated".
The force said its officers were at the ground "due to intelligence regarding a previous game between Chesterfield and Grimsby Town, where there was public disorder and members of the public were injured".
It added none of its officers were involved in any of the searches "which were carried out by stewards".